Of course, correlation does not equal causation. And there may be other demographic or systemic factors at play that influence performance in high versus low pollution environments. That said, this particular study followed the same individuals year over year, and revealed substantive differences in performance in the same individuals depending on how high air pollution levels were at the time.

While this study adds weight to the general—weirdly controversial—idea that we should cut air pollution and transition to a clean economy as fast as is humanly possible, it also suggests that there would be gains to be made from more targeted measures. Banning idling school buses, reducing car traffic around schools and other measures aiming to reduce localized pollution could pay significant dividends in terms of urban area test scores.

Still, the ultimate answer will be to tackle this problem everywhere. At least, that would be the smart thing to do...